Generating sets (“Gensets”) are used to provide electricity for distributed power generation systems, which include prime power, standby generation, and network support. Deregulation of electrical utilities has resulted in many customers utilizing their standby diesel gensets to improve power quality or to avoid peak electricity tariffs.
Gensets often consists of a diesel engine, a synchronous machine, and two controllers (a speed governor and an automatic voltage regulator (“AVR”)). Some of the modern microprocessor based AVR's are implemented with the Proportional, Integral, and Derivative (PID) control for stabilization and various supplemental control systems which include many limiters, VAR/PF controller, tuning functionality, protection and monitoring features.
The genset's output frequency is directly proportional to the diesel engine's speed. The speed governor seeks to maintain the diesel engine at a constant speed. The speed governor is designed to respond to changes in engine speed, acting as a feedback controller which controls the fuel rate to minimize a speed excursion due to a sudden change in the genset's real power load. Unlike the large size generators, many gensets may be expected to change operation from unloaded to full load in a single step load application, which causes large changes in engine speed or may cause the engine to stall.
International Standard ISO8528-5; 2013 provides a means to assess diesel genset performance, which classifies a genset based on a series of key performance indicators. For the modern gensets with G2 classification, the maximum voltage deviation from the nominal setpoint for a sudden load acceptance shall not exceed 20%, and the maximum electrical frequency deviation shall not exceed 10%. Voltage recovery time must be less than 6 seconds and frequency recovery time be less than 5 seconds. While some diesel genset controllers are able to meet the requirements of ISO8528-5; 2013, such controllers are expensive to manufacture.
A common way to reduce the engine speed drop is to provide an additional voltage dip during speed drops. Thus, faster engine speed recovery is achieved by reducing the real power load. Various voltage setpoint adjustments (under-frequency schemes) are used in modern AVR's. A load adjustment scheme has been suggested which temporarily reduces the voltage during a transient and therefore aids engine speed recovery. However, the speed governor's reaction to an engine speed change is much slower than the real power change. As such, the inventor hereof has identified a need for a system and method that can reduce the engine speed deviation of a genset when the real power load changes.